Typically, flexo printing is performed using a printing machine like the one as illustrated in FIG. 3. This printing machine includes a plate cylinder 51, an anilox roll 52, an ink supply device 53, a scraper 54, and a print stage 55. The plate cylinder 51 has a columnar shape, and a printing plate P1 is mounted to the plate cylinder 51. The anilox roll 52 is configured to cause ink to adhere to the printing plate P1. The ink supply device 53 is configured to supply the ink to a surface of the anilox roll 52. The scraper 54 is configured to scrape off surplus ink from the surface of the anilox roll 52. The print stage 55 is configured to receive a printing material Q subjected to printing.
The flexo printing using the printing machine is performed in the following manner. Specifically, the printing plate P1 is mounted to a peripheral surface of the plate cylinder 51. While the plate cylinder 51 is rotated, ink supplied from the ink supply device 53 is caused to adhere to a print region of the printing plate P1 through the anilox roll 52. The adhering ink is transferred to the printing material Q such as a glass board placed on the print stage 55, thereby performing printing. At this time, the print stage 55 is caused to slide in synchronization with the rotation of the plate cylinder 51.
Typically, as illustrated in a plan view of FIG. 4A and in a sectional view of FIG. 4B taken along the line T-T of FIG. 4A, the printing plate P1 includes a base portion 11 having a flat plate shape and a printing projection portion 12 formed at a center portion of a surface of the base portion 11. The printing projection portion 12 is the print region, and a portion of the base portion 11 surrounding the printing projection portion 12 is not involved in printing. Further, as illustrated in FIG. 4C being an enlarged sectional view of main portions of FIG. 4C, a plurality of projections 13 with gaps 14 are formed in a distributed manner on a top surface of the printing projection portion 12, and the ink is retained in the gaps 14. The printing plate P1 is flexible so that the printing plate P1 can be mounted to the peripheral surface of the plate cylinder 51 (see FIG. 3).
However, in the flexo printing, the printing projection portion 12 of the printing plate P1 is brought into contact with the anilox roll 52 and the printing material Q. Thus, the pressure generated at the time of contact causes the ink retained on the printing projection portion 12 to move to a peripheral edge region 12D of the printing projection portion 12. Therefore, such action causes occurrence of a so-called “marginal phenomenon” in which a thickness of the printing film formed by the flexo printing becomes larger at the peripheral portion surrounding the center portion than at the center portion.
Therefore, in order to suppress the occurrence of the marginal phenomenon, the applicant of the present application has proposed a printing plate in which a distribution density of the projections 13 formed on the printing projection portion 12 is set higher in the peripheral edge region 12D than in a center region 12A of the printing projection portion 12, and has filed patent applications related to such printing plate (for example, see Patent Literatures 1 and 2). That is, in the peripheral edge region 12D of the printing projection portion 12, the distribution density of the projections 13 is set higher to have smaller gaps 14 of the projections 13, thereby reducing the amount of ink retained in the gaps 14. With such a configuration, the thickness of the printing film at the peripheral edge portion is prevented from becoming larger. According to the printing plates in Patent Literatures 1 and 2, the distribution density of the projections 13 in the peripheral edge region 12D of the printing projection portion 12 is set equal at printing direction portions 12B extending along a printing direction (rotation direction of the plate cylinder 51) and at perpendicular direction portions 12C extending along a perpendicular direction perpendicular to the printing direction (direction parallel to a rotary axis of the plate cylinder 51).